From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sun, 8 Jul 2001 13:02:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sun, 8 Jul 2001 13:02:19 -0400 Received: from [194.213.32.142] ([194.213.32.142]:9988 "EHLO bug.ucw.cz") by vger.kernel.org with ESMTP id ; Sun, 8 Jul 2001 13:02:07 -0400 Date: Sat, 30 Jun 2001 15:37:41 +0000 From: Pavel Machek To: Jason McMullan Cc: linux-kernel@vger.kernel.org Subject: Re: VM Requirement Document - v0.0 Message-ID: <20010630153740.A59@toy.ucw.cz> In-Reply-To: <20010626155838.A23098@jmcmullan.resilience.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0.1i In-Reply-To: <20010626155838.A23098@jmcmullan.resilience.com>; from jmcmullan@linuxcare.com on Tue, Jun 26, 2001 at 03:58:38PM -0400 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi! > Here's my first pass at a VM requirements document, > for the embedded, desktop, and server cases. At the end is > a summary of general rules that should take care of all of > these cases. > > Bandwidth Descriptions: > > immediate: RAM, on-chip cache, etc. > fast: Flash reads, ROMs, etc. Flash reads aresometimes pretty slow. (Flash over IDE over PCMCIA...2MB/sec bandwidth. Slower than most harddrives. > medium: Hard drives, CD-ROMs, 100Mb ethernet, etc. CDroms are way slower than harddrives (mostly to seek times). > slow: Flash writes, floppy disks, CD-WR burners > packeted: Reads/write should be in as large a packet as possible > > Embedded Case > ------------- > > Overview > -------- > In the embedded case, the primary VM motiviation is to > use as _little_ caching of the filesystem for reads as > possible because (a) reads are very fast and (b) we don't > have any swap. However, we want to cache _writes_ as hard > as possible, because Flash is slow, and prone to wear. > > Machine Description > ------------------ > RAM: 4-64Mb (reads: immediate, writes: immediate) MB not Mb. 4Mb = 0.5MB. > Flash: 4-128Mb (reads: fast, writes: slow, packeted) > CDROM: 640-800Mb (reads: medium) > Swap: 0Mb > > Motiviations > ------------ > * Don't write to the (slow,packeted) devices until > you need to free up memory for processes. > * Never cache reads from immediate/fast devices. Flash connected over PCMCIA over IDE is *very* slow. You must cache it. -- Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt, details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.